The invention relates to cathodically depositable aqueous electrodeposition coating materials and to a process for coating electrically conductive substrates, in which
(1) the substrate is immersed in a cathodically depositable aqueous electrodeposition coating material, PA0 (2) the substrate is connected as cathode, PA0 (3) using direct current, a film is deposited on the substrate, PA0 (4) the coated substrate is removed from the electrodeposition coating material, and PA0 (5) the deposited coating film is baked.
Cathodically depositable, aqueous electrodeposition coating materials and the above-described process for coating electrically conductive substrates are known (cf. e.g. EP-B-301 293, DE-A-35 18 732, DE-A-35 18 770, EP-A-4090, EP-A-12 463, EP-A-262 069, U.S. Pat. No. 3,799,854, U.S. Pat. No. 4,031,050, U.S. Pat. No. 4,252,703, U.S. Pat. No. 4,332,711, DE-A-31 08 073, DE-A-27 01 002, EP-A-59 895, DE-A-31 03 642 and DE-A-32 15 891). Cathodic electrodeposition coating using cathodically depositable, aqueous electrodeposition coating materials has become established as a process for the automatic coating of bulky products, in particular vehicle bodies. Advantages of electrodeposition coating using cathodically depositable, aqueous electrodeposition coating materials are, for example, its environmental friendliness (water as solvent), very good material yield and high reliability with extensive automation of plants.
The present invention is based on the object of providing new cathodically depositable, aqueous electrodeposition coating materials which give coats having improved properties, in particular with regard to the formation of runs (runouts, boilouts), sensitivity to drops of water, and bridging.
Interfering runs can be formed if, during the baking process, electrodeposition coating material emerges from, for example, seams and runs down the coated surface. When the substrates present are of complex shape (e.g. V-shaped metal sheets) the emerging electrodeposition coating material may solidify in the form of bridges. In this case, bridging defects are the result. If--prior to the baking process--water or diluted electrodeposition coating material drips onto the electrodeposition coating film which, although not yet baked, has dried superficially, then, in the case of electrodeposition coating films with a high sensitivity to water drops, water-spotting defects can be seen after baking.
It is often attempted to eliminate the defects described above by adding surfactants. However, in many cases the addition of surfactants results in new interfering side-effects, for example the formation of foam and/or delamination of coatungs applied subsequently.
The present invention is based in particular on the object of eliminating as far as possible the defects described above without producing new interfering side-effects, for example the formation of foam and/or delamination of coatings applied subsequently.
This object is surprisingly achieved by adding, to cathodically depositable, aqueous electrodeposition coating materials known per se, particles of wax having a diameter of from 1 to 20 .mu.m. When incorporating the particles of wax into the electrodeposition coating material, those skilled in the art can employ all methods known to them for incorporating particulate additives into electrodeposition coating materials. It is preferred to incorporate the particles of wax in powder form or in the form of a dispersion in water, in a water-miscible organic solvent or in a mixture of water-miscible organic solvents into the pigment paste.